Method for establishing a motor vehicle operating variable that is to be determined

ABSTRACT

The invention relates to a method for establishing an operating variable to be determined of a motor vehicle in dependence on a first known operating variable and a second known operating variable, using a characteristics map for executing functions of the motor vehicle. Said characteristics map is stored in the Cartesian coordinate system in an electronic control device with the help of interpolating points. If a mathematically invertible characteristics map by which means an operating variable to be determined for a first motor vehicle function is entered on the Z-axis is provided, then by reverse interpolation using the same characteristics map, an operating variable allocated to the Y- or X-axis can also be an operating variable to be determined for a second motor vehicle function, the operating variable allocated to the Z-axis being the known operating variable for the second motor vehicle.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a method for determining a motor vehicleoperating variable that is to be determined.

A method of this type is known, from the technical handbook“Autoelektrik, Autoelektronik am Otto-Motor”, Robert Bosch GmbH, 1994particularly in connection with electronic control units for executinginternal-combustion engine functions. In this technical handbook, forexample, a characteristic diagram is illustrated on Page 163(Illustration 2), by which the advance angle is determined as a functionof the rotational speed and the load as known operating variables. Acharacteristic diagram is illustrated on Page 165 (Illustration 6), bywhich the closing angle is defined for controlling an ignition coil as afunction of the rotational speed and the battery voltage as knownoperating variables.

In principle, the surface of such a characteristic diagram in theCartesian coordinate system (X, Y, Z axes) consists of a network ofsupport points. Four support points respectively form a rectangularsurface element in the space. The lines of the rectangular surfaceelement in the space extend in parallel to the X-axis and Y-axis. Inorder to create such a regular structure of the support points or of thesurface of the characteristic diagram consisting of rectangles, thesupport points or the characteristic diagram data may only partially bebased on real measured values. If measured values are determined whichdo not correspond directly to the supporting points of a characteristicdiagram, the pertaining values in the Z direction are determined bymeans of linear interpolation.

The characteristic diagrams required for motor vehicle functions areformed experimentally and are stored in an electronic control unit forthe internal-combustion control, which is required anyhow. For eachdependence, a characteristic diagram is stored: Z=f (X, Y).

Normally, the operating variable to be determined is assigned to theZ-axis. The operating variable assigned to the X-axis and the Y-axis,respectively, are first and second operating quantities in the form ofinput quantities, particularly measuring signals. A characteristicdiagram of this type is normally stored for a defined motor vehiclefunction. Although frequently the same operating variables are processedfor additional motor vehicle functions, for example, the operatingvariable assigned to the Z-axis can now be known, but the operatingvariable assigned to the X-axis or the Y-axis may have to be determined;that is, one of the input variables of a characteristic diagram canbecome the output variable, but the output variable of a characteristicdiagram can become the input variable. In the case of the methodaccording to the prior art, a separate characteristic diagram was storedfor each of these cases, in which case the operating variable to bedetermined is always assigned to the Z-axis. As a result, highapplication expenditures and an immense storage space demand arecreated.

It is an object of the present invention to improve a process of theabove-mentioned type such that the application expenditures as well asthe storage space demand are reduced.

This object is achieved by a method for determining a motor vehicleoperating variable to be determined (M; t_(L)) as a function of a firstknown operating variable (n; M) and of a second known operating variable(t_(L); n) using a characteristic diagram stored by means of supportpoints in the Cartesian system of coordinates (X, Y, Z axes) in theelectronic control unit, for carrying out motor vehicle functions. Whena mathematically invertible characteristic diagram is present, by meansof which, for a first motor vehicle function, an operating variable (M)to be determined is entered on the Z axis, for a second motor vehiclefunction, by means of reverse interpolation by the same characteristicdiagram, an operating variable (t_(L)) to be assigned to the Y axis or Xaxis may also be a operating variable to be determined when, for thesecond motor vehicle function, the operating variable (M) assigned tothe Z axis is the known operating variable.

The use of one and the same characteristic diagram is essential to theinvention, irrespective of to which axis of the coordinate system theoutput quantity is assigned as the operating variable to be determined.If the operating variable to be determined corresponds to the operatingvariable assigned to the Z-axis, the conventional approach is used.However, if the operating variable assigned to the Z-axis becomes theknown operating variable, a reverse interpolation of the characteristicdiagram takes place. The prerequisite is a mathematical invertibility ofthe characteristic diagram; that is, the characteristic diagram mustextend monotonically in the X-direction and/or in the Y-direction.

As a result of the method according to the invention, the errorprobability is also reduced by decreasing manual expenditures.

The drawing illustrates an embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of the reverse interpolation according tothe present invention, for the example of two surface elements of acharacteristic diagram in the cartesian coordinate space;

FIG. 2 is a diagrammatic view utilizing the characteristic diagramaccording to the prior art;

FIG. 3 is a schematic view of two motor vehicle functions with differentcharacteristic diagrams according to the prior art; and

FIG. 4 is a view of two motor vehicle functions with one and the samecharacteristic diagram using the method according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

In FIGS. 1 to 4, the method according to the invention is explained incomparison to the prior art with reference to characteristic diagramsfor motor vehicle functions that are assigned to an electronicinternal-combustion engine control unit. In FIGS. 1 and 2, the air flowt_(L) is plotted on the X-axis, the rotational speed n is plotted on theY-axis, and the torque M of the internal-combustion engine is plotted onthe Z-axis. By means of the six supporting points x₁/y₂, x₁/y₃, x₂/y₂,x₂/y₃, x₃/y₂, and x₃/y₃, two surface elements A and B of acharacteristic diagram are set up as examples in the space. If, for afirst motor vehicle function, the air flow t_(L) and the rotationalspeed n are defined as input signals and thus as known operatingvariables, in a conventional manner, particularly when the values of theknown operating variables x and y are situated between the supportingpoints, the value z of the torque M is determined by means of linearinterpolation as the operating variable to be determined (compare FIG.2).

If a characteristic diagram according to FIG. 1 and FIG. 2 is presentand, if, for a second motor vehicle function, the torque M is the knownoperating variable but the air flow t_(L) is the operating variable tobe determined, a reverse interpolation according to FIG. 1 takes placeaccording to the invention. Since the characteristic diagram cutoutdefined by the surface elements A and B is monotonically decreasing inthe X-direction, the characteristic diagram can be mathematicallyinverted with respect to the X-axis. For the reverse interpolation, thesurface elements A and B of the characteristic diagram in the space areprojected onto the plane set up by the Y and Z-axes as surface elementsA′ and B′. As a result of the values y and z of the known operatingvariables, i.e., the rotational speed n and torque M, an intersectingpoint is obtained also in the plane set by the Y-axis and the Z-axis. Itis examined in which projected surface element A′ or B′ thisintersecting point (resulting from the values y and z) is situated. Inthis example, it is in the surface element B′. By means of a retransferof the surface element B′ including the intersecting point into thespace, it can finally be determined where this intersecting point issituated on the surface element B in the space. By way of the now knownlocation of the intersecting point in the space, again by means oflinear interpolation, in a known manner, if the intersecting point isnot situated on a support point, the X-value of the air flow t_(L)operating value to be determined, which is assigned to this intersectingpoint in the space, can be determined.

In the example according to the state of the art in FIG. 3, for a firstmotor vehicle function, the air flow t_(L) and the rotational speed nshould be known operating variables and the torque M is to be theoperating variable to be determined. Corresponding to the example ofFIG. 2, the torque M can be determined in the conventional manner fromthe first characteristic diagram 1. This determined torque M can bechanged in a torque coordination block 2, for example, by changing thedesired torque by operating the accelerator pedal into a new value M′.In a second motor vehicle function, the air flow t_(L) must now bedetermined as a function of the now known operating variables for therotational speed n and torque M′. According to the prior art, a secondcharacteristic diagram 3 is stored for this purpose, in which the airflow operating variable t_(L) to be determined is assigned to theZ-axis. Therefore, according to the prior art, two differentcharacteristic diagrams 1 and 3 are required for two motor vehiclefunctions, which each operate by means of two out of three identicaloperating variables.

With respect to the two motor vehicle functions, FIG. 4 shows the sameexample as FIG. 3. However, in contrast to FIG. 3, the samecharacteristic diagram as the first characteristic diagram 1 for thefirst motor vehicle function can be used for the second motor vehiclefunction. The new torque M′ as the output signal of the torquecoordination block 2 is entered as the input signal along with the knownoperating variable rotational speed n into the characteristic diagram 1.Subsequently, the determination of the air flow t_(L) takes place asdescribed in conjunction with FIG. 1.

Thus, instead of two characteristic diagrams, only one characteristicdiagram must be stored in the example according to FIG. 4, whereby theestablishment of a second characteristic diagram as well as the storagespace demand of a second characteristic diagram are saved.

What is claimed is:
 1. A method for determining a motor vehicleoperating variable to be determined as a function of a first knownoperating variable and a second known operating variable, the methodcomprising the acts of: accessing a mathematically invertiblecharacteristic diagram for motor vehicle functions stored via supportpoints in a cartesian coordinate system in an electronic control unit,by which mathematically invertible characteristic diagram an operatingvariable to be determined for a first motor vehicle function is enteredon a Z-axis of the cartesian coordinate system; reverse interpolatingsaid mathematically invertible characteristic diagram such that anoperating variable allocated to the Y- or X-axis becomes an operatingvariable to be determined for a second motor vehicle function, saidoperating variable allocated to the Z-axis becoming one of the first orsecond known operating variables for determining the second motorvehicle function; wherein one and the same characteristic diagram isstored in the electronic control unit for determining the operatingvariable for the first and second motor vehicle functions.
 2. The methodaccording to claim 1, wherein, for said reverse interpolation, surfaceelements of the characteristic diagram in the space formed by thesupport points are projected onto a plane of the Z-axis and anadditional axis, to which the operating variable to be determined is notassigned, and subsequently examining in which projected surface elementan intersecting point of the values of the known operating variables issituated, and where said intersecting point is finally situated in apertaining surface element in the space.
 3. A method for determiningmotor vehicle operating variables that are to be determined as afunction of first and second known operating variables using acharacteristic diagram stored in a cartesian coordinate system with theaid of interpolation points in an electronic control unit, the methodcomprising the acts of: using a mathematically invertible characteristicdiagram for motor vehicle functions, stored in the cartesian coordinatesystem for determining an operating variable for a first motor vehiclefunction that is on the Z-axis, for determining an operating variablefor a second motor vehicle function allocated to the Y- or X-axis usingreverse interpolation of said stored mathematically invertiblecharacteristic diagram, in which the operating variable on the Z-axisfunctions as one of said first and second known operating variables;wherein one and the same characteristic diagram is stored in theelectronic control unit for determining the operating variable for thefirst and second motor vehicle functions.